1. Field of the Invention
This invention relates to a powered seat adjusting device to be used for adjusting seats in automobiles and the like, and more particularly to a type thereof, wherein the position of the vehicle seat can be adjusted forwardly or rearwardly by use of an electric motor or the like.
2. Description of the Related Art
FIG. 1 illustrates a conventional powered seat adjusting device comprising an upper rail 11 secured to a seat (not shown), a lower rail 12 secured to the floor (not shown) of a vehicle, a nut 13 secured to the upper rail 11, a screw-threaded shaft 15 engaging with the nut 13, a housing 14 provided on the lower rail 12 for rotatably supporting the screw-threaded shaft 15 through bearings 17, a worm wheel 16 formed integral with the screw-threaded shaft 15, and a worm gear (not shown) meshing with the worm wheel 16. When the worm gear is rotated by an electric motor (not shown) or the like, the screw-threaded shaft 15 is rotated through the worm wheel 16, thereby shifting the nut 13 secured to the upper rail 11 and hence to the seat forwardly and rearwardly in accordance with the rotating direction of the electric motor or the like. When the operation of the motor terminates, the seat is maintained at a position determined by the engagement of the worm wheel 16 and the worm gear (not shown).
In the above described conventional device, since the screw-threaded shaft 15 is formed integral with the worm wheel 16, any load applied in the forward and rearward direction to the seat is transmitted through the upper rail 11 and the nut 13 to the screw-threaded shaft 15, thus displacing the same forwardly or rearwardly. The displacement of the shaft 15 inevitably misaligns the engagement between the worm wheel 16 and the worm gear entailing the creation of frictions and noises, and in a worst case damaging the worm wheel 16 and/or the worm gear. For preventing such difficulties, the strength of the housing 14 must be increased so as to eliminate the displacement of the screw-threaded shaft 15, which gives rise to a disadvantage of increasing the size of the housing 14.